The structural evolution and microwave dielectric properties of (1-x)Li2TiO3 + xMgO system (x = 0.0-0.5) compounds were investigated. The degree of ordering decreased with increasing MgO content. The ...microcracks and cleavage on (001) due to the weak Li-O bonds disappeared with increasing MgO content. The dielectric constant and temperature coefficient of resonant frequency decreased with increasing MgO content. The Qxf value increased with x up to x = 0.2 and then decreased with further increase of x. Excellent combined microwave dielectric properties could be obtained when x = 0.24, epsilonr = 19.2, Qxf = 106226 GHz and tauf = 3.56 ppm/C.
Perfluoroalkoxy (PFA) composites filled with different volume fractions of hollow glass microsphere (HGM) and HGM/PFA–HGM/HBO3–HGM/PFA sandwich layered composites were prepared by simple dry mixing ...and hot‐pressing process. The dielectric frequency and temperature response characteristics, thermal expansion coefficient, and mechanical strength were investigated as a function of the loading fraction of HGM fillers. The obtained .6VfHGM/.4VfPFA composite demonstrates ultralow‐k (εr ∼ 1,63@1 MHz; 1.57@10 GHz) with low‐dielectric loss (∼7.2 × 10−4@1 MHz; ∼1.73 × 10−3@10 GHz), water absorption of ∼1.21%, in‐plane thermal expansion coefficient of 42 ppm/°C, and temperature coefficient of dielectric permittivity (τεr) of ∼−92 ppm/°C. The temperature stabilities of dimension and dielectric permittivity for the .6VfHGB/.4VfPFA composite could be substantially improved by forming .6VfHGM/.4VfPFA–.6VfHGM/.4VfHBO3–.6VfHGM/.4VfPFA sandwich–layered composite, which still maintained reasonable dielectric properties and mechanical rigidity with flexural strength of ∼8.1 MPa.
The influences of CuOLi
2
CO
3
additive on the sintering behaviors, microstructure, and dielectric/piezoelectric/ferroelectric properties of a commercial "soft" lead zirconate titanate (PZT)-based ...piezoelectric ceramic have been investigated in this paper. The sintering temperature of PZT ceramic could be successfully reduced to 1050 °C with the addition of 0.1 wt% CuOLi
2
CO
3
. The possible sintering mechanism and sintering kinetics were studied based on the in situ measurement of temperature dependent sintering shrinkages of the samples. Some Cu/Li ions incorporated into the perovskite lattice and the remainder precipitated as Pb-rich secondary phase by eutectic formation at triple junction of grain boundaries. Cu
+
seems to be more likely to enter into the perovskite lattice in comparison to Cu
2+
, leading to a little smaller
ε
r
, tan
δ
,
d
33
and high temperature conduction
.
The addition of CuOLi
2
CO
3
leads to an increase in the concentration of rhombohedral phase around the morphotropic phase boundary (MPB) composition, resulting in decreases in permittivity, dielectric loss, piezoelectric coefficient (
d
33
)
, and coercive field (
E
c
), slight increase in remnant polarization (
P
r
), while little change in
T
c
temperature (~ 310 °C) and electromechanical coupling coefficient (
k
p
). Good combined dielectric and piezoelectric properties with
ε
r
= 1881, tan
δ
= 1.32%,
d
33
= 474 pC/N and
k
p
= 0.73 could be obtained with the addition of 0.4 wt% CuOLi
2
CO
3
after sintering at 1050 °C/2 h.
Satellite observations have shown that the Asian Summer Monsoon strongly influences the upper troposphere and lower stratosphere (UTLS) aerosol morphology through its role in the formation of the ...Asian Tropopause Aerosol Layer (ATAL). Stratospheric Aerosol and Gas Experiment II solar occultation and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar observations show that summertime UTLS Aerosol Optical Depth (AOD) between 13 and 18 km over Asia has increased by three times since the late 1990s. Here we present the first in situ balloon measurements of aerosol backscatter in the UTLS from Western China, which confirm high aerosol levels observed by CALIPSO since 2006. Aircraft in situ measurements suggest that aerosols at lower altitudes of the ATAL are largely composed of carbonaceous and sulfate materials (carbon/sulfur elemental ratio ranging from 2 to 10). Back trajectory analysis from Cloud‐Aerosol Lidar with Orthogonal Polarization observations indicates that deep convection over the Indian subcontinent supplies the ATAL through the transport of pollution into the UTLS. Time series of deep convection occurrence, carbon monoxide, aerosol, temperature, and relative humidity suggest that secondary aerosol formation and growth in a cold, moist convective environment could play an important role in the formation of ATAL. Finally, radiative calculations show that the ATAL layer has exerted a short‐term regional forcing at the top of the atmosphere of −0.1 W/m2 in the past 18 years.
Key Points
Increase of summertime upper tropospheric aerosol levels over Asia since the 1990s
Upper tropospheric enhancement also observed by in situ backscatter measurements
Significant regional radiative forcing of −0.1 W/m2
Abstract Hydrogen sulfide (H2 S) is a naturally occurring gas that may act as an endogenous signaling molecule. In the brain, H2 S is mainly produced by cystathionine β-synthase (CBS) and its ...cellular effects have been attributed to interactions with N -methyl- d -aspartate (NMDA) receptors and cyclic adenosine 3′,5′-monophosphate (cAMP). In contrast, direct vasodilator actions of H2 S are most probably mediated by opening smooth muscle ATP-sensitive K+ (KATP ) channels. In the hypothalamus, KATP channel-dependent mechanisms are involved in CNS-mediated regulation of blood pressure. In this report, we investigated the hypothesis that H2 S may act via KATP channels in the hypothalamus to regulate blood pressure. Mean arterial blood pressure (MAP) and heart rate were monitored in freely moving rats via a pressure transducer placed in the femoral artery. Drugs were infused via a cannula placed in the posterior hypothalamus. Infusion of 200 μM sodium hydrogen sulfide (NaHS), an H2 S donor, into the hypothalamus of freely moving rats reduced MAP and heart rate. Infusion of 300 nM to 3 μM gliclazide dose-dependently blocked the effect of 200 μM NaHS. Infusion of the CBS activator, s-adenosyl- l -methionine (0.1 mM and 1 mM), likewise decreased MAP. Infusion of the CBS inhibitors aminooxyacetic acid (10 mM) and hydroxylamine (20 mM) increased MAP but did not block the effects of infusion of 200 μM NaHS. These data indicate that actions of H2 S in the hypothalamus decrease blood pressure and heart rate in freely moving rats. This effect appears to be mediated by a KATP channel-dependent mechanism and mimicked by endogenous H2 S.
To assess the feasibility of a radiomics model based on unenhanced magnetic resonance imaging (MRI) to differentiate small hepatocellular carcinoma (S-HCC) (≤2 cm) and pre-hepatocellular carcinoma ...(Pre-HCC).
One hundred and fourteen histopathologically confirmed 114 hepatic nodules were analysed retrospectively. All patients had undergone MRI before surgery using a 3 T MRI system. Each nodule was segmented on unenhanced MRI sequences (T1-weighted imaging T1 and T2WI with fat-suppression FS-T2). Radiomics features were extracted and the optimal features were selected using the least absolute shrinkage and selection operator (LASSO). The support vector machine (SVM) was used to establish the radiomics model. One abdominal radiologist performed the conventional qualitative analysis for classification of S-HCC and Pre-HCC. The diagnostic performances of the radiomics and radiologist models were evaluated using receiver operating characteristic (ROC) analysis.
Radiomics features (n=1,223) were extracted from each sequence and the optimal features were selected from T1, FS-T2, and T1+FS-T2 to construct the radiomics models. The radiomics model based on T1+FS-T2 showed the best performance among the three models, with areas under the ROC curves (AUCs) of 0.95 (95 % confidence interval CI, 0.875–0.986) and 0.942 (95 % CI, 0.775–0.985), accuracies of 86 % and 88.5 %, sensitivities of 94.12 % and 100 %, and specificities of 85.48 % and 85.19 %, respectively. The radiomics model on FS-T2 showed better performance on a single sequence than that of the T1-based model. The diagnostic performance for the radiomic model was significantly higher than that for the radiologist (AUC = 0.518, p<0.05).
This study suggested that a radiomics model based on unenhanced MRI may serve as a feasible and non-invasive tool to classify S-HCC and Pre-HCC.
•Radiomics based on T1+ FS-T2 can classify small-HCC and pre-hepatocellular carcinoma.•This study focuses on the identification of small-HCC and pre-hepatocellular carcinoma.•Radiomics model based om FS-T2 shows better performance than that of T1.•Radiomics model shows better performance than that of conventional qualitative analysis.•All lesions have the histopathological results as reference standard.
Abstract Cerebral hypoxia is one of the main causes of cerebral injury. This study was conducted to investigate the potential protective effect of H2 S in in vitro hypoxic models by subjecting ...SH-SY5Y cells to either oxygen–glucose deprivation or Na2 S2 O4 (an oxygen scavenger) treatment. We found that treatment with NaHS (an H2 S donor, 10–100 μM) 15 min prior to hypoxia increased cell viability in a concentration-dependent manner. Time-course study showed that NaHS was able to exert its protective effect even when added 8 h before or less than 4 h after hypoxia induction. Interestingly, endogenous H2 S level was markedly reduced by hypoxia induction. Over-expression of cystathionine-β-synthase prevented hypoxia induced cell apoptosis. Blockade of ATP-sensitive K+ (KATP ) channels with glibenclamide and HMR-1098, protein kinase C (PKC) with its three specific inhibitors (chelerythrine, bisindolylmaleide I and calphostin C), extracellular signal-regulated kinase 1/2 (ERK1/2) with PD98059 and heat shock protein 90 (Hsp90) with geldanamycin and radicicol significantly attenuated the protective effects of NaHS. Western blots showed that NaHS significantly stimulated ERK1/2 activation and Hsp90 expression. In conclusion, H2 S exerts a protective effect against cerebral hypoxia induced neuronal cell death via KATP /PKC/ERK1/2/Hsp90 pathway. Our findings emphasize the important neuroprotective role of H2 S in the brain during cerebral hypoxia.
Current evidence suggests that hydrogen sulfide (H2S) plays an important role in brain functions, probably acting as a neuromodulator as well as an intracellular messenger. In the mammalian CNS, H2S ...is formed from the amino acid cysteine by the action of cystathionine β-synthase (CBS) with serine (Ser) as the by-product. As CBS is a calcium and calmodulin dependent enzyme, the biosynthesis of H2S should be acutely controlled by the intracellular concentration of calcium. In addition, it is also regulated by S-adenosylmethionine which acts as an allosteric activator of CBS. H2S, as a sulfhydryl compound, has similar reducing properties as glutathione. In neurons, H2S stimulates the production of cAMP probably by direct activation of adenylyl cyclase and thus activate cAMP-dependent processes. In astrocytes, H2S increases intracellular calcium to an extent capable of inducing and propagating a “calcium wave”, which is a form of calcium signaling among these cells. Possible physiological functions of H2S include potentiating long-term potentials through activation of the NMDA receptors, regulating the redox status, maintaining the excitatory/inhibitory balance in neurotransmission, and inhibiting oxidative damage through scavenging free radicals and reactive species. H2S is also involved in CNS pathologies such as stroke and Alzheimer's disease. In stroke, H2S appears to act as a mediator of ischemic injuries and thus inhibition of its production has been suggested to be a potential treatment approach in stroke therapy.
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